<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{margin: 0;padding: 0;}
        .header{
            width: 100%;
            height: 500px;
            background-color: red;
        }
        .nav{
            width: 500px;
            height: 49px;
            background-color: green;
            margin: 0 auto;
            position: sticky;
            top: 36px;
        }
        .body{
            width: 100%;
            height: 1024px;
            background-color: blue;
        }
    </style>
</head>
<body>
    <div class="header"></div>
    <div class="nav"></div>
    <div class="body"></div>
</body>
</html>